Several methods have been proposed for providing optical fiber glass materials on the inner surface of disposable cylindrical mandrels. One such method is that described within copending application Ser. No. 804,208, filed June 7, 1977, in which the glass constituents are chemical vapor deposited on the interior surface of a carbon mandrel and the carbon mandrel is later removed by combustion.
Another method for depositing glass constituents on a disposable mandrel is described within U.S. application Ser. No. 804,209 filed June 7, 1977. This application teaches a method of chemical vapor depositing glass constituents upon the interior surface of a split carbon mold. The mold is subsequently opened and the glass constituents are removed in tubular form for processing into a fiber optic preform.
The method of depositing glass constituent materials on the inner surface of carbon molds is not readily conducive to the mass production of fiber optic materials since some additional means of providing a travelling hot zone is usually required to insure that the glass forming constituents will deposit uniformly on the interior mold surface. The above identified applications, incorporated herein by way of reference, utilize the resistive properties of the mold to provide a portion of the heat required for the thermal decomposition of the chemical vapor materials involved and also utilize an auxillary travelling hot zone.
The methods which propose deposition of the glass forming constituents on the exterior surface of a refractory mandrel usually involve drilling away the mandrel once the glass materials have been consolidated into a solid continuous cylinder or use the refractory substrate as a bait in the fiber drawing process.